Frocks- for resolotiom of sacemic glu



United States Patent Ofihce 25,359 PROCESS. FOR RESOLUTION OF RACEMIC GLU- TA'MIC ACHDAND SALTS THEREUF Tetsuo Ogawa, Tokyo, and Takekazu Alrashi, Kawasakishi, Kanagawa-ken, Japan, assignors to Ajinomoto (10., Inc., Tokyo, Japan, a corporation of Japan Original No. 2,949,998, dated June 14, 1960, Ser. No. 710,015, Jan. 20, 1958. Application for reissue June 11, 1962, Ser. No. 203,687

Claims priority, application Japan Get. 15, 1953 15'Claims. (Cl. 260?.-534l) Matter enclosed in heavy brackets If appears in the original patenthut forms no part of this reissue specifi ,cation; matter printed in italics indicates the additions made by reissue.

This. invention. relates generally to processes for the resolution of racemic glutamic acid andsalts thereof, in order to obtain the optical isomers of the racemic compounds, and this application is a continuation-in-part of our prior application Serial No. 462,366, filed October 14, 1954, and now abandoned.

L-glutamic .acidis a well known seasoning material .used in cooking and the like. Since chemical processes for the synthesis of glutamic acid result in the formationof its racemic modification, namely DL-glutamic acid, cheap and simple methods for resolution of DL-glutamic acidaare especially important in this field. Although it has been. proposed to Elproduced] produce L-glutamic acidby. resolution of DL-glutamic acid through the vuseof chemical and biochemical reagents, these procedures have a number of disadvantages for industrial purposes, in that they require the use of rather expensive reagents and usually involve many tedious and troublesome operations. It has been also proposed to resolve DL-glutamic acid by physiochemical or mechanical methods, but such methods also have many disadvantages, such as, poor reproducibility. of the same result and low efficiency of resolution.

Accordingly, it is an object of the invention to provide a commercially practical process for resolving racemic glutamic acid and salts thereof, in order to obtain the highest possible yield of the desired optical isomers during the shortest possible operating period.

In accordance with anraspect of the present invention, racemic glutamic acid, that is, DL-glutarnic acid, is resolved into its optical isomers by seeding an aqueous supersaturated solution of the racemic glutamic acid withcrystals of one of the isomers thereof to cause the corresponding isomer in the supersaturated solution to crystallize out ofthe solution. It has been found that the efficient resolution .of racemic glutamicacid into its .optical isomers. L-glutalnic acid and D-glutamic acid requires .thatthe rate of crystallization of the optically active glutamic acid or. salts thereof be maintained under a predetermined maximum, and that the crop, or total amount ofithe optically active isomer crystallized during each stage of'the process must also'be held belowa predetermined maximum value based upon the total quantity of racemic glutamic acidor salts thereof-contained in the solution which is to be resolved.

Accordingly, it is another object of the invention to determine those-maximum limits of the rate of crystallization and of the total crystallization which must be maintained in a commercially acceptable process.

Anotherobject of this invention is to facilitatesupersaturation of solutions of racemic glutamic acid intended for resolution into its optical'isomers by utilizing racemic glutamic acid monohydratc and a bottom solid or solid phase in the solution at a temperature higher than the Reissued Mar. 26, 1963 transition point between the monohydrate and anhydrate.

form, so that the monohydrate causes supersaturation of the solution, and thereby facilitates and simplifies the resolution of racemic glutamic acid.

Another objectof this invention is to provide processes for the resolution of racemic glutamic acid and salts thereof applicable over a relatively wide range wherein conglomerate type racemic salts of glutamicacid and double-salt-type racemic glutamic acids are included, but complex-salt type racemic glutamate is excluded.

A further object of the invention is to provide a reliable semi-continuous process for resolving racemic glutamic acid, racemic salts of glutamic acid, such as, racemic glutamic acid hydrochloride, or racemic monoammonium glutamate.

The above, and other objects, features and advantages of the invention, will be apparent in the following detailed description and in the illustrative examples thereof.

In the accompanying drawing:

FIG. 1 is a graph showing the solubilities of glutamic acid and'its salts at 30 C. for various degrees of acidity and alkalinity; and

FIG. 2 is a graph showing the solubility'of racemic glutamic acid, racemic glutamic acidmonohydrate and L-glutamic acid at various temperatures.

In accordance with the present invention, whereby racemic glutamic acid is resolved into its optical isomers by seedingan aqueous supersaturated solution of the racemic glutamic acid with crystals of one of the isomers to cause the corresponding isomer in the supersaturated solution to crystallize out, it hasbeen found that the rate of crystallization should be controlled to less than 7.5% per hour of the total quantity of racemic glutamic acid in the solution and thatthe total crystallization should be limited to not more than an amount corresponding to 25% of the total quantity of glutamic acid in the solution.

The above maximum rate of crystallization of optically active .glutamic acid .or its salts is. applicable to each of the hereinafter mentioned. methods of' effecting supersaturation, such as, by .themonohydrate as a bottom solid, or. by cooling, evaporation or partial neutralization. Which of .these methods of supersaturating' the solution is adopted. depends upon thekinds of racemic glutamic acid or its salts contained in the raw material to be treated, their concentration, their phase (solid or liquid), temperature and the like.

The rate of crystallization of optically active glutamic acid and glutamates is dependent upon the rate of cooling, rate of partial neutralization or rate of concentration (evaporation), where such means are employed for effecting supersaturation, or upon the maintained temperature of the solution supersaturated by a bottom solid of the monohydrate. The-rate of crystallization increases as the rate of cooling, rate of partial neutralization or rate of evaporation is gradually increased until the rate of crystallization reaches 7.5% per hour. But, after the rate of'crystallization reaches 7.5% per hour, fur.- ther increases in the rate of cooling, partial neutralization or evaporation do not further increase the rate of crystallization, but, on the contrary,.serve to decrease .the latter.

Similarly, it has beenfound that the maximum amount of crystallization of. optically activeglutamic acid and glutamates resolved-in each stage corresponds to about 25% of the total racemicglutamicacid or glutamates in the solution. Above-that limit, even if further resolution is attempted by means of further cooling, partial neutralization or evaporation, the crystallization of optically active glutamic acid and glutamates is diminished, while be operated at temperatures in the ranges shown in the following table:

Means for SurG rG rG 4 persaturatlng Cooling 20-80 C. (opt. 2080 C. (opt. 2060 O. (opt.

30-60 0.). 30450 O. 3060 0.). Evaporation, 20-60 O. (opt. 2060 0. (opt. 20-60 C. (opt. Part. neutr. 20-30 C 2(]30 0.). 30-40 0.). Monohydrate 22i2 C.50

O. (opt. 25- 40 0.).

In general cooling is a convenient means of effecting supersaturation, while partial neutralization is eitective in cases where the concentration of racemic glutamic acid in the solution is comparatively high, and evaporation may be adopted in cases where the concentration is comparatively low. On the other hand, the use of racemic glutamic acid monohydrate as a bottom solid has the advantage of automatically maintaining the supersaturated condition of the solution as the seeded isomer crystallizes out.

Further, it has been bound that D-glutamic acid and L-glutamic acid form, in the neutral range, complex-salt type racemic compounds (monoalkali glutamates), which have the strongest association or linkage between the two isomers, but that the association is weakened gradually in proportion to the added quantities of mineral acids or alkalies. Thus, a double-salt type racemic compound is formed in the range of free glutamic acid, while conglomerates of both isomers are formed either in the range of mineral acid salts thereof or in the range of dialkalisalts thereof and even in the ranges containing addition quantities of mineral acids or alkalies.

It has been further found that a solid capable of existing at the bottom in a solution of glutamic acid, water and either mineral acid or alkali is racemic glutamic acid in the state of a double-salt type which forms two kinds of crystals, one of them existing as the anhydrate at temperatures higher than 22 C12 C., the transition point, while the other exists as the monohydrate at temperatures lower than said transition point of 22 C.- +-2 C.

The temperature coefficient of solubility of the monohydrate is remarkably higher than the corresponding coemcient of optically active glutantic acids, while the temperature coelficient of solubility of the anhydrate is slightly smaller than said coeflicients of optically active glutamic acids, as illustrated in FIG. 2. In other words, the heat of solution of the monohydrate is considerably higher than those of optically active glutamic acids, while that of the anhydrate is slightly lower than those of optically active glutamic acids. Resolution processes according to this invention may utilize either the alkaline or acidic range of solutions of heterogeneous univariant equilibrium systems consisting of three components which are racemic glutamic acid, Water and mineral acid or alkali, and containing the monohydrate of racemic glutamic acid as bottom solid in the solution.

If a saturated solution of the above mentioned heterogeneous univariant equilibrium system consisting of the three components and containing monohydrate of racemic glutamic acid as the bottom solid therein in either the acidic or the alkaline range is inoculated with fine seed crystals of one of the two isomers of optically active glutamic acid at a temperature higher than 22 C.J C., the same isomer as the seed crystals gradually crystallizes out from the solution, leaving the antipode in the solution saturated with racemic glutamic acid. At such time, the solid monohydrate cannot remain as such and gradually dissolves into the solution as the isomer crystallizes out. In other words, the supersaturated state, that is, equilibrium between racernic glutamic acid monohydr ate as the solid in the solution and racemic glutamic acid as one of the solutes is broken by crystallization of the isomer and dissolution of the monohydrate into the solution occurs at the same time. Thus, crystallizing out of one of the optical isomers and dissolving in of the monohydrate of racernic glutamic acid occur simultaneously and continuously so that the supersaturation of the solution with racemic glutamic acid is maintained and the resolution is carried out continuously.

It is important that the monohydrate, which is stable only at a temperature lower than 22 C.i2 C., be used as the solid phase in the solution at a temperature higher than 22 C.- :2 C., that is, in the region where the anhydrate crystallizes out. In consequence of this, the solution becomes supersaturated with regard to the anhydrate, thereby giving rise to an enormous potential for crystallization of optically active glutamic acid, and moreover the presence of the monohydrate crystals makes the supersaturation regarding the anhydrate remarkably stable.

However, if the operation is carried out at too high a temperature in an attempt to further increase the degree of supersaturation due to the monohydrate bottom solid, crystallization of the anhydrate is apt to occur and this obstructs the resolution of racemic glutamic acid.

The most preferable range of temperatures for the process of resolution employing the monohydrate as a bottom solid has been found to be approximately between 25 C. and 40 C., between which temperatures an adequate degree of supersaturation due to the monohydrate as the bottom solid may be maintained, while the tendency towards crystallization of the anhydrate is comparatively low. More specifically, the above process for resolution of racemic 'glutamic acid may be carried out as follows:

A supersaturated solution containing racemic glutamic acid, water and mineral acid or alkali, as the solutes and the solvent, and racemic glutamic acid monohydrate as the bottom solid in said solution is first prepared. The supersaturated solution-is then inoculated with one of the two isomers of racernic glutamic acid, and the inoculated solution is vigorously stirred while being maintained at a temperature higher than approximately 22 C. and lower than approximately 50 C. The developed crystals of the same isomer as that with which the solution was inoculated are collected, for example, by filtration. Racemic glutamic acid monohydrate is added to the remaining clear mother liquor to restore the supply of bottom solid. The solution is then inoculated with the antipode of the previously obtained optically active glutamic acid. Following vigorous agitation of the solution, and maintenance of the temperature, within the above limits, the developed crystals of the same isomer as those employed for the second inoculation are collected. Cyclical repetition of the above steps may be applied to the clear mother liquor in a semicontinuous fashion.

The principle of the above described procedure may be applied to the resolution of racemic glutamic acid in a process wherein the supersaturated state of the solution is obtained by means of evaporation, cooling or partial neutralization or the like rather than by the use of the monohydrate as a bottom solid.

As previously mentioned, it has been found that D and L+glutamic acidsvform, in neutral range, complexsalt' type racemic. compounds (monoalkali glutamates), which have the strongest association'between the two isomers, but that theassociation becomes Weaker gradually. in proportion to the added quantities of mineral acids for example, hydrochloric acid or sulfuric acid, or alkalies, for example, sodium hydroxide or potassium hydroxide, with a double-salttype racemic compound being formed in the range of free glutamic acid'while conglomerates of both isomers are formedeither in the range of mineral acid salts thereof or in the range of dialkali salts thereof. Racemic. glutamic acid in the range of the double salt type compound has been found to be also capable of being resolved by supersaturating the heterogeneous .univariant equilibrium system consisting of racemic glutamic acid, water and mineral acid or alkali, inoculating or seeding said solution with one of the isomers of the racemic acid, stirring said solution, maintaining the supersaturated solution by means of concentration, cooling or partial neutralization rather than by the previously describedmonohydrate as the bottom solid, collecting the developed crystals of seeded isomer, supplementing the supply of racemic glutarnic acid, supersaturating the solution, inoculating it with the antipode, of the first seeded-isomer, stirring the solution, maintaining the supersaturated state ofthe solution, collecting the developed crystals of :the antipode and repeating the steps in succession. The preferable temperature for the process ranges from approximately 20 C., that is, room temperature, to about 80C.

Racemic glutamic acid hydrochloride is also capable of being resolved in a Way similar to that described above, except that racemic glutamieacid hydrochloride is usedinstead of free race'mic glutamic acid in preparing the supersaturatedsolutionand supplementing the racemic compound. The preferable temperature for the process of resolving racemic glutamieacid hydrochloride also ranges from roomtemperature to about 80 C.

Application of a similar process to racemic dialkali glutamates gives extremely fine crystals of optically active glutamate in an extraordinarily viscous solution and is therefore unfavorable for industrial purposes.

It has also been found thatracemic monoammonium glutamate can be resolved in a similar way, except that racemic monoammonium glutamate is used in lieu of free glutamicacid or its hydrochloride in preparing the supersaturated solutionand in supplementing the racemic compound. The preferable temperature for this process ranges from room temperature to about 60 C. However, the resolution process embodying this invention is notapplicable to racemic monoalkali glutamates which are complex-salt type compounds.

In connection with the mineral acids or alkalies included in the solutions formed initially in the above described methods, the solubilities of racemic glutamic acidchange remarkably in proportion to the-quantities of such mineral .acids or alkalies.

Racemic glutamic acid is only slightly soluble water, but the solubility increases remarkably by the addition of quantities of mineral acids or alkalies which are over 6.0% of the amounts of mineral acidsror alkalies theoretically necessary, to-neutralize an equivalent of glutamic acid, and reachesmaximum when neutralization is accomplished. But the solubility of glutamic acid is again reduced to a very low value by the addition of quantities of mineral acids which are over twelve times as much as the amount of mineralacid theoretically necessary to neutralize an equivalent of glutamic acid.

In accordance with this. invention, best resolution results are generally obtained with solutions having high concentrations of glutamic acid or its salts. Consequently, in order to obtain good results, it has-been found that the amount of mineral acids in the solution should be at least between 0.6 and 10, and preferably between 0.8 and 5.0, equivalents per mole of DL-glutamic acid in the solution, whi1e,,in the caseof solutions containing alkalies, the. latter should be present in 'amounts at least between 0.6 and 1.0,. and preferablybetween 0.8 and 1.0, equivalents per mole of Dlrglutamic acid.

As shown in FIG. 1, theabove relative. amounts of mineral acids and alkaliescorrespond to ranges of pH values between approximately 0'.2.21X1(l 2.0 and. between .approximately 4.0 and 7:0, respectively In general, the stability ofasupersaturated solution of either racemic glutamic acid, that is, DL-glutamic acid, or itssaltsdecreasesas the temperature.is.elevated. In other-words, .the tendency towardscrystallization of either racemie glutamic acid .orracemic, saltsthereof from a supersaturated solution-thereofincreases withelevation of temperature. Therefore, the ,solutionemployed in the resolving process should be maintained at a temperature lower. than the upper limitsqspecifiedineach case described above.

Development or growth of the optically active glutamic acid or salts thereof isrcmarkably iacceleratedby turbulence of the supersaturated solution caused by1agitating, stirring, mixing or the. like. Thus, producing "turbulence is oneof theimportant conditions necessary in carryingv outthe, process for: resolution; according-to this invention.

EXAMPLE 1 I and was filtered after 5 hours, to obtain:

In the above steps, the rate of crystallization was controlled at about. 1.7% per hour, and the obtained crop was about 8% of the total racemic glutamic acid .in the solution.

19.0 g. of 5% H01 aqueous solution were added to the crystals and the mixture was filteredafter agitation. The separated crystals were lightly washed with water and dried, to obtain 6.0 g. of pure L-glutamic acid (total nitrogen 9.52%, (a) =+31:6).

(B) To the 148 g. of the mother-liquor (total glutamic acid 30.0%, D-glutamic acid 2.24%),WCI'C added 15.7 g. of racemic glutamic acid monhydrates (total-nitrogen 8.49%; (ot) =i0;00"?), containing 14.01;.v of anhydrous glutamic acid, as a solid phase andSLO .g. of pure D- glutarnic acid (total nitrogen 9.53%, (a) =3.1.6) as .crystal seeds. Thesolution was ept at 301' C. While being stirred and wasfilte-red after 8 hours.

Crystals (dry), 18.7 g (d) '=21.4 Mother liquor, g a -+0.-s4

In the above step, the rate of crystallization Was controlled at about 2.2% per hour,- and the obtained crop was about 17% of the total quantityofracemic glutamic acid in the solution.

33.0 g. of 5%. HCl aqueous solution was added to the crystals and the mixture was filteredafter agitation. The separated crystals werelightly washed .with water and dried. 10.9 g. of crystals of pure D.-.glutamic acid (total nitrogen 9.51%, (a) -=-31.2) was. thus obtained.

When a similar operation was performedunder the 7 same conditions, except that the temperature was 17 C. instead of 30 C. and total glutamic acid about 26% instead of 29.2% in 150 g. of the filtrate, the following was obtained:

Crystals (dry), 11.0 g (a) =+lO.2 Mother liquor, 149 g (a) =i0.0

The above rotation for the crystals was due to the crystal seeds, and the rotation for the mother liquor indicated no presence of the antipode, and hence no resolution. All that was obtained were the crystal seeds and the added racemic glutamic acid monohydrate.

Another similar operation was performed under the same conditions, with the exception that the temperature was 60 C. and total glutamic acid was 33% in 150 g. of the filtrate, and the following was obtained:

Crystals (dry), g (m) =+1l.l Mother liquor, 148 g (a) =i0.0

The rotation indicated for the crystals was due to the crystal seeds and the rotation for the mother liquor indicated no presence of the antipode, and hence no resolution. In this comparative experiment too, all that was obtained was the crystal seeds, and the added racemic glutamic acid monohydrate was converted into anhydrate.

EXAMPLE 2 Crystals (dry), 7.0 g (a) =|-20.5 Mother liquor, 142.0 g (a) =-0.56

In the above step, the rate of crystallization was controlled at about 3% per hour, and the obtained crop was about 12.5% of the total racemic glutamic acid in the solution. 7

The crystals were mixed with 13.5 g. of 5% HCl aqueous solution and the mixture was filtered after agitation. The separated crystals were lightly washed with water and dried, to obtain 3.8 g. of pure L-glutamic acid (total nitrogen 9.51%; (a) =+31.2).

(B) To the 142 g. of mother liquor (total glutamic acid 14.1%; D-glutamic acid 1.75%; pH 4.9) were added 10.1 g. of racemic glutamic acid monohydrate- (total nitrogen 8.49%; (a) =i0.00), containing 9.0 g. of anhydrous glutamic acid, as a bottom solid or solid phase; and 4.5 g. of D-glutamic acid (total nitrogen 9.53%; (a) =-3l.6) as crystal seeds. The solution was kept at 30 C. while being stirred and was filtered after 7 hours, to obtain:

Crystals (dry), 13.5 g (a) =22.O Mother liquor, 141.5 g (a) =|-0.52

rated crystals were lightly washed with water and dried,

to obtain 8.4 g. of crystals of pure D-glutamic acid (total nitrogen 9.53%, (a) =-31.6).

The following specific Examples 3 to 6 of the invention illustrate the use of cooling to elfect supersaturation for resolution:

EXAMPLE 3 200 g. of 6.5% H01 aqueous solution saturated with racemic glutamic acid monohydrate (total nitrogen 8.49%; (a) =i0.00) was prepared at 45 C. and filtered. The filtrate (total glutamic acid 24.2%) was inoculaited or seeded with 1.5 g. of L-glutamic acid (total nitrogen 9.53%; (u) =+3l.6) and allowed to cool at a rate of 5 C. per hour with vigorous stirring. After cooling down to 30 C. requiring 3 hours, the solution was kept at that temperature for 2 hours and filtered. The crystalline L-glutamic acid was washed with a small quantity of water and dried, to obtain: Crystals, 5.6 g. (net wt. 4.1 -g.), (a) =+3l.6 (pure).

In the above step, the rate of crystallization was about 1% per hour and the crop was about 6% of the total racemate.

The mother liquor was mixed with racemic glutamic acid (total nitrogen 9.53%; (a) =1-0.00) and heated to a temperature of 56 C. When almost saturated, it was filtered instantly. The filtrate (total glutamic acid 25.8%) was inoculated with 1.5 g. of D-glutamic acid (total nitrogen 9.53%; (u) =-3l.6) and allowed to cool at a rate of 5 C. per hour with vigorous stirring. After a treatment similar to that described above for L-glutamic acid, the obtained D-glutamic acid was: Crystals, 9.3 g. (net wt. 8.8 g.) (u) =-31.3 (pure).

In the above example, the rate of crystallization of optically active glutamic acid was about 23% per hour and the crop was about 14% of the total racemate. In comparative experiments, the rate of crystallization was increased by raising the rate of cooling from 5 C. per hour to 12-13 C. per hour, with resulting rates of crystallization of 67% per hour. In these experiments, the

net Weight of optically active crystals was found to be 8.3 g. when it was attempted to increase the rate of crystallization of optically active glutamic acid to reach 9% and 12% per hour, that is, beyond the limit of 7.5% per hour, by further increasing the rate of cooling to 20 C. and 26 C. per hour, respectively, the rate of crystallization of optically active glutamic acid dropped to 7% and 4.5% per hour and the net weight of optically active glutamic acid actually obtained decreased to 6.3 g. ail 4.0 g., respectively, as indicated in the following ta 1e:

Dry Rate of crys- Rate of cool- Cooling Total sub tallizatlon of ing O./hr.) time crop stance (a)n optical isomer (hr.) (g.) (g.) (percent per hour) 5 9. 3 8. 8 -31. 3 about 23 2 9. 0 8. 3 -31. 4 6-7 1. 3 8. 6 6. 3 -30. 5 7 1 7. 9 4. 0 30. 4 4. 5

Further comparative experiments were made with respect to the previously indicated limit of 25% concerning the total crystallization in each stage of the operation in relation to the total quantity of glutamic acid as follows:

Total quantity of optical isomer crys- Dry Subtallized in each stage as a percent of Total stance ((1)13 the total racemic glutanu'c acid in crop (g.) (optical) the solution (percent) isomer) weight of optically active glutamic acid actually obtained was only 6.0 g.

EXAMPLE 4 200 g. of 5.05% NaOH aqueous solution'saturated with racemic glutamic acid anhydrate (total nitrogen 9.53%; (a) =:0.00) was prepared at 45 C. and;

filtered. The filtrate (total glutamic acid 18.3%; pH 5.0-) was inoculated with 1.5 g. of L-glutamic acid (total nitrogen 9.5 3%; (a) =+3l.6) and allowed to coolat.

a rate of 5 C. per hour with vigorous stirring. After cooling, down to 30 C. requiring 3 hours,- the solution was kept at that temperature for 1 hour and then-filtered. The crystalline L-glutamic acid was washed with a small quantity of'water and dried to obtain: Crystals 5.2 g. (net wt. 3.7 g.), (a) =-|3l.4 (pure).

In the above step, the controlled rate of crystallization was 1-2% per hour, and thecrop. w as 6% ot the total racemate,

The mother liquor was mixed with racemic glutamic acid (total nitrogen 9.53%; (M -110.00") and heated toa temperature of 56 C. When almost saturated, it was filtered instantly. The filtrate (total glutamic acid 19.7%) was inoculated with, 1.5 ug. ofiD-glutarnic acid (total nitrogen 9.53%; =-31.6" and allowed to cool at a rate of 5 C. per hour withgvigorous stirring. After a treatment similar to that described. abovein connection with the L-glutamic acid, the obtained D-glutamic acid was: Crystals 8.2 g. (net wt. 7.2 g.), (u) =31.5 (pure).

In theabovestep, the controlled rate of. crystallization was about 154% per hour, and the crop obtained was about 14% of the total racemate.

EXAMPLE 5 40 g. of a clear saturated solution of racemic. monoammonium. glutamate monohydrate (total nitrogen present in the form of NH; and NH being each 7.7%; (a) =i 0.00), containing 59% of said glutamate as its anhydrate, was prepared. at 40 C. Said solution was inoculated with 1,0 g, of L'-monoammonium glutamate monohydrate (total nitrogen present intheform of NH and NH being each 7.7% (a) =+25.8) and allowed to cool at a rate of 35 C. per hour with continuous stirring. Wh n cooled down to 31 C., the solution was filtered, to obtain: Crystals, 4.5 g., (a) =-|15.7.

In the above step, the controlled rate of crystallization was about 24% per hour, and the crop was about 7% of the total racemate.

The mother liquor was mixed with racernic monoammoniurn glutamate monohydnate and heated to a temperature of 46 C. When almost saturated, it was filtered instantly. The filtrate (total content of saidamrnonium glutamate 63% as anhydnate thereof) was inoculated'with 1.0 g. of D-rnonoammonium glutamate monohydrate (total nitrogen present in the form Of-NH; and NH; being'each 7.7% (a) =25.8) and allowed to cool at a rate of 3 5 C. per hour with continuous stirring. When cooled down to 30 C., it was filtered to obtain: Crystals, 7.0 g., (a);. =l7.0.

In the above step, the controlled rate of crystallization was about 2,5-5% per hour, and the crop was about 14% of the total racemate.

Both of the above. kinds of-crystals resulted in almost pure active monoammonium glutamate monohydrates (total nitrogen present in the form of NI-L; and-NH being each 7.7% in each case; (a) =+25.7O' or 10 -25 .7 when mixed .with a quantity of water just sufficient to dissolve the racemic glutamate accompanied by said active glutamates and .then filtered...

EXAMPLE 6 50 g. of a clear saturated solutionof racemic glutamic aci rhy rochloride. .(totalglu arni ci hydrochloride 49%) was prepared at 45 C. The above solution was inoculated with 1.0 g. of L-glutarnic acid hydrochloride (total nitrogen 7.62%; (a) 25.6) and allowed to cool at a rate of 5 C. per hour with continuous stirring. Whencooled down to 33 C., the. solution was filtered to obtain: Crystals, 4.8 g., (a) =-|-20.D.".

In the above step, the controlled rate of crystallization was about 5 per hour, and the crop Wasabout 11% otthe total racemate in; the solution.

The mothe quid;(t tal. lu arnic acid hydrochloride 45%; D-glutarnic acid hydrochloride 5.97%) was mixed with. racemic glutamic. acid hydrochloride (total nitrogen 7.62%; (00 :1001?) and heated to atemperature of 56". C. When almost saturated, it was filtered instantly. The filtrate (total glutamic acid hydrochloride 51.7%; D-glutamic acid hydrochloride 5.0 9%) was inoculated with 1.0 g. ofD-glutamic acid hydrochloride .(total nitrogen 7.62%; (op) =25.6) and allowed to cool at a rate of 5 8? C. per hour with continuous stirring. When cooled down -to 32 C., the solution was filtered'to obtain: Crystals, 7.9 g., (a) =18.6.

In the above step, the controlled rate of crystallization 'was about 4 6% per hour, and the obtained crop was about 18% of the total racernate (racemic glutamic acid) in the solution.

Both of the above kinds of crystals-resultedin almost purewactive glutamic acid. hydrochlorides (total nitrogen 7.61% foreaeh; (00 +255 or 25.6, respectively),

when mixed with a quantity of water lust sufficien-t to dissolve the racemic hydrochlorideaccompanied by the active hydrochloride and then filtered.

In. comparative experiments, range of temperatures for cooling inthe above example was variously changed as follows:.

Total (04) D25, quantity Range of temperature Crop. g. degrees of optical isomer. Do een? from 56 to 32 C 7. 9 l8. 6 18 from 39 to 20 C 6.5 17. 7 14 l'rom20t0 4 C"... 4.0 16.6v r 8 from 791:0 65 0,", 7.3 -17. 5 12 from 92 to 81*. G 8:6 11. 6 7.5

The mother liquor separated in step (B) of Example in 4 sr nd' ng o atisn ()D +0- was further subjectedto asirnilar procedure. forrresolun l ushpr ced e wa epeate out n imes. The following table is a summary of the results obtained in the subsequent repeated steps of the process. Said steps (A) and (B) in Example 1 were numbered respectively l and 2.

Used Obtained Balance (isomer Step Racemie Oalcu- Isomer obtained monolated as Crystal (:)D, Total Isomer in by resohydrate, anhyseeds, g. degrees crop, g. crop, g. lution, g.)

g. drate, g.

7.85 7.0 3.5 L +21.0 11.0 7.2 3.7 15. 70 14.0 5.0 D -21.4 18.7 12.5 7.5 15. 70 14.0 5.0 L +20.8 10.1 12.4 7.4 15.70 14.0 5.0 D 20.7 10.1 12.4 7.4 15. 70 14.0 5.0 L +20.8 18.9 12.3 7.3 15. 70 14.0 5.0 D 20.0 15.0 12.2 7.2 15.7 14.0 5.0 L +21.2 12.7 12.4 7.4 15.70 14.0 5.0 D 20.0 18.7 12.2 7.2 15. 70 14.0 5.0 L +21.0 18.6 12.2 7.2 15. 70 14.0 5.0 D -20.8 18.8 12.2 7.2 15. 70 14.0 5.0 L +21.1 18.7 12.3 7.3

Totals 104.85 147.0 75.8

As illustrated in the above table 75.8 g. of active at 30 C. To 174 g. of the clear solution there were glutamic acid was obtained from 164.85 g. of racernic 20 added 30 cc. of an aqueous solution containing 4.7 g./dl. glutamic acid monohydrate containing 147 g. of racemic of potassium hydroxide at a rate of 20 cc. per hour under glutamic acid as its anhydrate. moderate agitation in order to effect supersaturation by EXAMPLE 8 partial neutralization. After 10 minutes since the beginning of the addition of potassium hydroxide, 3.5 g. of a Solution, containing 0f HC1 and of pulverized crystals of D-glutarnic acid were added to 24% 0f TaCemiC glutamic acid and bfilonging to the same the supersaturated solution as seeding crystals. Followrange as in Example 3, was subjected to the resolution ing filtering, washing and drying, there was Obtain procedure of that example, but on an industrial scale Crystals (1), 7.5 g., (a) :-Z6.0- in accordance with this invention. The quantities listed In the above, the rate of crystallization of D-glutamie in the following table for the additions of pure acid was controlled at about 3% per hour and the obracemic glutamic acid anhydrate (total nitrogen 9.53% tained crop was about 4.5% of the total quantity of (u) =i0.00) in ea h step, wer add d to the m th r racemic glutamic acid in the solution. To 190 g. of liquor of the preceding step and dissolved completely filtrate or mother liquor remaining after removal of the in the latter by heating at 6065 C. Upon sudden D-glutamic acid crystals, at 30 C. and containing 28.4% cooling to 48 C., 150 g. of pure L- or D-glutamic acid of whole glutamic acid, 1.29% of L-glutamic acid, 9.9% (total nitrogen 9.53%; (u) =+31.6 or 3l.6) was of sulfuric acid and 1.10% of potassium sulfate, there added to the solution in each step of resolution as cryswere added, while undergoing moderate agitation, tel seeds. The solution was allowed to cool gradually cc. of an aqueous solution containing 8.75 g./dl. of potasat a rate of 6 C. per hour. When cooled down to sium hydroxide over a period of 3 hours. 10 minutes 30 0., it was filtered and developed crystals were 001- 40 after the beginning of the addition of potassium hydroxlected. Crystals were washed with water, dried and ide, 3.5 g. of pulverized crystals of L-glutamic acid were analysed. The mother liquor in each step was adjusted added as seeding crystals. Following filtering, washing to provide 20 kg. and then subjected to the successive and y g, there Was Obtained: Crystals 14 steps of the process. The following table is a summary ()D of the results obtained in the subsequent steps of the In this Step, the fate of crystallization of L-gllltamic process repeated fift en time acid was controlled at about 4% per hour and the obtained crop was about 12% of the total quantity of race- Used Obtained mic glutamic acid in the solution. The crystals (1) and (2) obtained, as above, were washed separately as in Ex- Step Racemic Isomer Home, ample 1, and the purse crystals weighed:

gli t aglie (50D, Total in Crop. af fi degrees ggg $285 D-glutannc ac d, 5.5 g (u) =31.4 grams L-glutam1c aCld, 9.8 g (u) =+31.1

0.78 L +2110 0.80 0.74 M LE 10 0.80 D -28.4 0.81 0.72 3-33 4728-4 71 At values of pH below 7.0, glutamic acid forms water- -2s.s 0. 79 0.71 080 L M8 072 soluble salts w1th alkali earth metals in the same way as 8% B ig- 82 8-33 with alkali metals. For the formation of such gluta- (12530 D h g mates, either hydroxides or carbonates of either alkali 8-58 fig-g gg 8- metals or alkali earth metals may be used. Calcium car- 1 1 1 bonate was therefore adopted in this example which em- 3-33 23- 3;? 8-2 ploys evaporation to efiect supersaturation. D 1 1 1 As W111 be apparent from the table in Example 7, the L 5 52 5 operations from the 2nd step onward should be considered .01 Total 11.18 5 ormal running under ordinary operating COfldltlOnS. In D 5.53 the present example, however, a quantity of L-glutamic acid was added to the original solution in order to effect As shown in the above table, 11.18 kg. of racemic normal running from the beginning, that is, during the glutamic acid anhydrate was resolved into 5.52 kg. of first step or crystallizing stage. L-compound (5.01 kg. of L-glutarnic acid) and 5.53 kg. 70 T0 20 g. of about a 2% aqueus solution of L-glutamic of D-compound (5.01 kg. of D-glutarnic acid). acid, 80 g. of racemic glutamic acid and 20 g. of CaCO were added. The resulting solution was stirred at 55 E 9 C. for 1 hour and then filtered. The filtrate had a glu- An aqueous solution containing 34.5% of racemic tamic acid concentration of 16.7%, while L-glutamic acid glutarmc acid and 12.2% of sulfuric acid was prepared 75 content was 1. 02% and its pH was 4.5.

To 350 g. ofsuch filtrate, 7 g. of L-glutamic acid (pu-v rity,.94%) a n d 50 cc. of aqueous racemic glutamic acid solutionof 5 g./d l. (concentration) was added. The foregoing mixture wasconeentrated, in vacuum, ata rate of evaporation of 4070 cc./hr. by heating it at 55-60" C. Every hour, 50 cc. race rnicgultamic acid solution of g. /d1. (concentration) was supplied and observations wereintermittently made with respect to specific rotation.

When the concentrated solution was filtered after 4 hoi1 r s,,200 ,cc. of said .r acemic glutarnic acid solution had been added and 212cc. of water had been avaporated, and the following was obtained: Crystals, g., (a) .r+25.2.

The operation Wascontrolled at a rate of crystallization of about 12.2% per hourand a total crystallization of about 9% lot total glutamic acid' Am lltihthc above, specific examples have been inherein to illustrate ,theinyention, it is to be understood that. the invention is not limited to such examples, except'as defined in thelappended claims What. is ,claimedfis:

1.'A method. for resolving, DL-glutamic acid into its optical isomers which: comprises forming an aqueous saturated solutionofIDL-glutamid acid having a pH value within,the ranges'ofapproximately 0.2 and 2.0 and approximately llt) and 7.0, respectively, adding DL-glutarnic acid monohydrate to an aqueous saturated solution of DL-glutamic acid at a temperature within the range between the transition point of said monohydrate to anhydrate and approximately 50C., so that said monohydrate formsa bottom solidin said solution to supersaturate thelatter, seeding said supersaturated solution with crystals of one of said isomers and agitating to cause said one isomer. to crystallize out of said supersaturated solution While maintaining the latter at a temperature within said range so that said monohydrate progressively enters into said solution. to maintain the supersaturated condition of the latteras said'one isomer is crystallized, filtering said solution to separate crystals containing said one isomer from the mother liquor, adding DL-glutamic acid monohydrate to said mother liquor to again form a supersaturated solution of the latter and to restore the supply of bottom solid therein, seeding the supersaturated solution with crystals of the other of said isomers and agitating to cause said other isomer to crystallize out of said supersaturated solution while maintaining the temperature of the latter within said range so that said monohydrate progressively enters into said solution to maintain the supersaturated condition of the latter as said other isomer is crystallized, and filtering the solution containing the crystallized other isomer for removing the latter, the crystallization of said one isomer and of said other isomer being controlled to occur at a rate having a maximum of 7.5 percent per hour of the total quantity of DL-glutamic acid in the solution in each case, and the total quantity of said isomers crystallized in each case corresponding, at most, to 25 percent of said total quantity of DL-glutamic acid in the respective solution.

2. A method for resolving DL-glutamic acid into its optical isomers which comprises forming an aqueous saturated solution of DL-glutamic acid having a pH value within the ranges of approximately 0.2 and 2.0 and approximately 40 and 7.0, respectively, thereby to obtain a relatively high concentration of DL-glutamic acid in said saturated solution, super-saturating said solution, seeding said supersaturated solution with crystals of one of said isomers to cause said one isomer to crystallize out of said supersaturated solution, agitating the seeded solution to facilitate the crystallization of said one isomer while maintaining said solution in supersaturated state at a temperature between C. and 80 C., controlling the rate of crystallization of said one isomer to a maximum of 7.5 percent per hour of the total quantity of DL-glutamic acid in the solution, and filtering the solution to recover said one isomer that has been crystallized therefrom following the crystallizing of a total quantity of said one isomer which corresponds, at most, to approximately 25pe rcent of said total quantity of DL-glutamic acid in the solution.

3 A method for resolving DL-glutamic acid into its optical isomers as in claim 2; wherein said solution is supersaturated by adding DL-glutami-c acid monohydrate to the saturated solution to provide a bottomsolid in the latter while maintaining the solution at a temperature in the range between approximately 25 C. and 40 C. so that said monohydrate enters into the solution to maintain the supersaturated condition of the latter as said one isomer is crystallized.

4. A method for resolving DL-glutamic acid into its optical isomers as in claim 2; wherein said saturated solution is supersaturated by cooling the latter at a rate of from 3 C. to 15- C. per hour,

5. A method for resolving DL-glutamic acid into its optical'isome rs as in claim 2; wherein said saturated solutionis supersaturated by evaporating some of the water therefrom.

6. A- method for resolvingDL-glutamic acid into its optica lisomers as in-claim 2; Whereinsaid saturated solution is supersaturated-by partially neutralizing said saturated solution.

7. A method for resolving DL-glutamic acid into its optical isomers comprising dissolving DL-glutamic acid in water and in a mineral acid'at a temperature between 20 C. and C. until a saturated solution is formed with the amount of said mineral acid therein being within the range of from 0.6 to 10 equivalents per mole of DL- glutamic acid,- supersaturating said solution, seeding said supersaturated solution with crystals of one of said isomers to cause said one isomer to crystallize out of said supersaturated solution, agitating the seeded solution to facilitate the crystallization of said one isomer-while maintaining said solution in supersaturated state at a temperature between-20- C. and 80 C., controlling the rate of crystallization of said one isomer to. a maximum of 7.5 percent per hour of the total quantity of DL- glutamic acid in the solution, and filtering the solution to recover said one isomer that has been crystallized therefrom following the crystallizing of a total quantity of said one isomer which corresponds, at most, to approximately 25 percent of said total quantity of DL-glutamic acid in the solution.

8. A method for resolving DL-glutamic acid into its optical isomers comprising dissolving DL-glutamic acid in water and in a soluble member of the group consisting of hydroxides and carbonates at a temperature of from 20 C. to 80 C., the amount of DL-glutamic acid being sufiicient to form a saturated solution at said temperature, said soluble member being present in proportions of from 0.6 to 1.0 equivalents per mole of DL-glutarnic acid, supersaturating said solution, seeding said supersaturated solution with crystals of one of said isomers to cause said one isomer to crystallize out of said supersaturated solution, agitating the seeded solution to facilitate the crystallization of said one isomer while maintaining said solution in supersaturated state at a temperature between 20 C. and 80 C., controlling the rate of crystallization of said one isomer to a maximum of 7.5 percent per hour of the total quantity of DL-glutamic acid in the solution, and filtering the solution to recover said one isomer that has been crystallized therefrom following the crystallizing of a total quantity of said one isomer which corresponds, at most, to approximately 25 percent of said total quantity of DL-glutamic acid in the solution.

9. A method for resolving DL-glutamic acid into its optical isomers as in claim 7; wherein said mineral acid is hydrochloric acid.

10. A method for resolving DL-glutamic acid into its optical isomers as in claim 7; wherein said mineral acid is sulfuric acid.

11. A method for resolving DL-glutamic acid into its optical isomers as in claim 8; wherein said soluble membet is sodium hydroxide.

12. A method for resolving DL-g1utamic acid into its optical isomers as in claim 8; wherein said soluble memher is calcium carbonate.

13. A method for resolving DL-glutamic acid into its optical isomers which comprises forming an aqueous saturated solution of DL-glutamic acid having a pH value within the ranges of approximately 0.2 and 2.0 and approximately 4.0 and 7.0, respectively, thereby to obtain! a relatively high concentration of DL-glutamic acid in. said saturated solution, super-saturating said solution, seeding said super-saturated solution with crystals of one of said isomers to cause said one isomer to crystallize out of said super-saturated solution, agitating the seeded solution! to facilitate the crystallization" of said one isomer while maintaining said solution in supersaturated state at a temperature between C. and 80 C., controlling the rate of crystallization of said one isomer to a maximum of 7.5 percent per hour of the total quantity of DL-glutamic acid in the solution, and collecting the crystals of said one isomer following the crystallizing of a total quantity of said one isomer which corresponds, at most, to approximately percent of said total quantity of DL-glutamic acid in the solution.

14. A method of resolving DL-glutamic acid into its optical isomers comprising dissolving DL-glutamic acid in water and in a mineral acid at a temperature between 20 C. and 80 C. until a saturated solution is formed with the amount of said mineral acid therein being within the range of from 0.6 to 10 equivalents per mole of DL- glutamic acid, supersaturating said solution, seeding said supersaturated solution with crystals of one of said isomers to cause said one isomer to crystallize out of said supersaturated solution, agitating the seeded solution to facilitate the crystallization of said one isomer while maintaining said solution in supersaturated state at a temperature between 20 C. and 80 C., controlling the rate of crystallization of said one isomer to a maximum of 7.5 per- 15 cent per hour of the total quantity of DL-glutamic acid in the solution, and collecting the crystals of said one isomer following the crystallizing of a total quantity of said one isomer which corresponds, at most, to approximately 25 percent of said total quantity of DL-glu'tamic acid in the solution.

15. A method for resolving DL-glutamic acid into its optical isomers comprising dissolving DL-glutamic acid in water and in a soluble member of the group consisting of hydroxides and carbonates at a temperature of from 20 C. to C., the amount of DL-glutamic acid being sufiicient to form a saturated solution at said temperature, said soluble member being present in proportions of from 0.6 to 1.0 equivalents per mole of DL-glutamic acid, supersaturating said solution, seeding said supersaturated solution with crystals of one of said isomers to cause said one isomer to crystallize out of said supersaturated solution, agitating the seeded solution to facilitate the crystallization of said one isomer while maintaining said solution in supersaturated state at a temperature between 20 C. and 80 C., controlling the rate of crystallization of said one isomer to a maximum of 7.5 percent per hour of the total quantity of DL-glutamic acid in the solution, and collecting the crystals of said one isomer following the crystallizing of a total quantity of said one isomer which corresponds, at most, to approximately 25 percent of said total quantity of DL-glutamic acid in the solution.

Gilrnan: Organic Chemistry, vol. I (1938), pages 187189.

Houben: Die Methoden der Organischen Chemie, vol. 2 (1943), page 1065.

Amiard et a1. Feb. 14, 1956 

